The image formed on the screen of most video monitors is produced by scanning an electron beam quickly across the back of the screen in a horizontal direction while also scanning the beam in a vertical direction, but at a slower rate. This process whereby the electron beam is scanned both horizontally and vertically is termed raster scanning. Along the inside surface of the monitor screen is provided a material which emits light when stimulated by the electron beam. To the electron gun which produces the electron scanning beam is provided a video signal comprising a serial stream of data pulses. Each pulse is associated with a different position along a scan line, and, depending upon the amplitude of the pulse, causes the associated screen point, referred to as a picture element or pixel, to emit light. The described raster scanning process is typically repeated at a rate of sixty scans per second.
In addition to the video signal which is provided to the electron beam gun, the logic circuit which drives the monitor must provide vertical and horizontal synchronization signals to control positioning of the scanning beam, and vertical and horizontal blanking signals to "turn off" the electron beam during scan retrace, i.e., while the scanning beam is returned to the beginning of a scan line or the top of the screen.
The scanning process discussed above relates to a monochrome monitor. Color monitors typically employ three light emitting materials on the inside of the monitor screen and scan three electron beams across the screen, the three materials emitting shades of red, blue and green light, respectively.
The resolution of a video screen is defined by the number of scan lines displayed multiplied by the number of pixels on each line. Television sets include monitors which have a resolution of 525.times.256 pixels. However, the need and desire to improve picture clarity and quality and to increase the amount of information which can be displayed by monitors coupled to personal computers, computer workstations, CAD systems and the like has resulted in the development of video controllers and monitors providing greatly increased image resolutions. For example, the video controller logic board included in the NCR X-Station terminal currently supports a monitor having a resolution of 1280.times.1024 pixels. However, in order to support other monitors having different resolutions and timing parameters it becomes necessary to alter the video controller logic through hardware changes, possibly designing and constructing a new controller board for each new monitor specification.